Clinton has faced significant criticism for previously using the word "super-predators," a now-debunked term that she said at the time referred to children with "no conscience, no empathy" who were committing crimes and had to be brought “to heel.”

At a campaign event in New York City earlier this week, Sanders jabbed Clinton for using the phrase, calling it "unacceptable."

“I think we all know what that term meant in the context that it was said years ago," he said. "We know who they were talking about.”

He took that criticism a step further when asked during the debate to explain why he had called Clinton out.

"Because it was a racist term, and everybody knew it was a racist term," he responded.

Sanders' jab came during a broader discussion about the 1994 crime bill, a piece of legislation that Clinton championed as first lady and that Sanders voted for as a member of the House. It is widely accepted that the law contributed to an era of mass incarceration by implementing harsh penalties for lower-level offenses, which had a disproportionate impact on communities of color and the poor.

On Thursday, Clinton said the law included positive aspects, like the Violence Against Women Act, but that the sentencing requirements of the bill were problematic.

"There were decisions that were made that now we must revisit and we have to correct," she said. "I think that sentences got much too long. The original idea was not that we would increase sentences for nonviolent low-level offenders, but once the federal government did what it did, the states piled on."

"I'm sorry for the consequences that were unintended and that have had a very unfortunate impact on people's lives," Clinton added.

Sanders largely agreed, suggesting that the bill's net impacts had been catastrophic.

"We have a broken criminal justice system," he said. "We have more people in jail than any other country on Earth. In my view, what we have got to do is rethink the system from the bottom on up."

Sanders then pivoted to drug policy, saying it was time to turn away from an approach that has for decades tried -- and failed -- to address drug use with strict punitive measures and aggressive law enforcement.

"We have got to have the guts to rethink the so-called war on drugs," he said. "Too many lives have been destroyed because people possess marijuana. Millions over a 30-year period. That's why I believe we should take marijuana out of the federal Controlled Substances Act."

Sanders has introduced legislation in the Senate to do just that. The bill would remove weed from the Drug Enforcement Administration’s list of the “most dangerous” drugs, giving states a green light to legalize pot for recreational or medical use without federal intervention. It would also allow for expanded research on the medical benefits of marijuana.